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1. Field of the Invention
This invention relates to the field of cushions. More specifically the present invention comprises a stratified cushion assembly which can be used to support the human body under various conditions.
2. Description of the Related Art
Many cushions and devices for supporting parts of the human body are known in the prior art. These devices come in many different designs and configurations. One example of such a device is described in U.S. Pat. No. 4,265,484 to Stalter (1981). Stalter describes a polyurethane formed body support member having a plastic reinforcing member and foam on either side of the plastic reinforcing member. The Stalter device utilizes the plastic reinforcing member to distribute the load evenly across the layer of foam under the reinforcing member.
Another cushioning device is exemplified by U.S. Pat. No. 5,294,181 to Rose et al. (1994). Rose et al. discloses a seat cushion made of layers of polyurethane foam, each layer having a different density. The Rose et al. device utilizes a sloping base layer to support an intermediate foam layer having a pair of laterally spaced recesses to accommodate the user's legs. A top layer having a range of protrusions and valleys is employed on top of the intermediate layer.
Other popular cushioning devices utilize visco-elastic memory foam to cushion and support the human body. Despite the growing popularity of visco-elastic foam, there are many disadvantages to using cushions made entirely of visco-elastic foam. First, visco-elastic foam is more expensive to manufacture than other foams. Second, cushions made of visco-elastic foam tend to “trench” around a user's body. This can make it difficult for the user to move around after sitting or lying in one place for an extended period of time. Finally, visco-elastic foam materials tend to trap heat and moisture more than other foams.
Many other cushions are known in the prior art, but are not discussed herein. Despite the existence of these types of cushions there remains a need for a low-profile cushion assembly that is supportive, comfortable, and that can be employed for a variety of cushioning applications.
The present invention comprises a “stratified” cushion assembly which can be used to support the human body under various conditions. The stratified cushion assembly generally includes alternating strata of supportive material, with each stratum having a different compression modulus than its adjacent strata. In the preferred embodiment the cushion assembly comprises alternating strata of visco-elastic memory foam and open-cell polyurethane foam. The strata are adhesively attached together with a foam adhesive.
FIG. 1 is an exploded view, showing an embodiment of the present invention.
FIG. 2 is a section view, showing an embodiment of the present invention.
FIG. 3A is a perspective view, showing an insert.
FIG. 3B is a perspective view, showing an insert.
FIG. 3C is a perspective view, showing an insert.
FIG. 4 is a perspective view, showing an alternate embodiment of the present invention.
FIG. 5 is an exploded view, showing the present invention.
FIG. 6 is a perspective view, showing the present invention.
FIG. 7 is a perspective view, showing the present invention.
The present invention, cushion assembly 10, is shown in FIG. 1. Cushion assembly 10 is of multilayer construction having top layer 22, middle layer 12, and bottom layer 14. In the preferred embodiment, the different layers are bonded together with glue or other adhesive. Top layer 22 is generally composed of a supportive material having a high compression modulus. Bottom layer 14 generally includes matrix 16 which is composed of a supportive material having a low compression modulus and a plurality of inserts 18 situated within matrix 16. Inserts 18 are preferably made of a supportive material having a high compression modulus. Middle layer 12 is situated between top layer 22 and bottom layer 14 and is preferably a woven material such as cloth. Although cloth is the preferred material, other deformable materials can be used that are relatively inextensible in the plane of the material.
Those that are skilled in the art know that a material's compression modulus is related to how “supportive” a material is, particularly a foam material. In the context of foam, the compression modulus relates to a foam's ability to support a force at different levels of displacement or compression. An approximation for a foam's compression modulus can be computed for a material by taking the ratio of the material's indentation force deflection (“IFD”) at 25 percent indentation (IFD25%) and 65 percent indentation (IFD65%) as shown in EQ. 1 below.
Compression Modulus for a Foam=IFD65%/IFD25% [EQ. 1]
Indentation force deflection is determined by taking the force in pounds required to indent or compress a piece of foam a specified percentage of its total height (typically a total height of 4 inches is used) with a surface area of 50 square inches. For example, a foam that has a IFD at 65% indentation of 100 pounds (meaning that the height is compressed 65% when subjected to a force of 100 pounds) and an IFD at 25% indentation of 50 pounds has a compression modulus of 2.0 (compression modulus values for polyurethane foam typically range from 1.8 to 3.0).
The compression modulus for polyurethane foam is a function of the density of the foam and the structure of the foam. Generally, the compression modulus increases as foam density increases. Also, different chemical formulations and manufacturing processes can be used to create foams with different cell structures. Foams with a high concentration of closed cells (closed-cell foam) typically have a higher compression modulus than foams with a high concentration of open cells (open-cell foam).
Returning to FIG. 1, top layer 22 and inserts 18 are preferably made of closed-cell polyurethane foam while matrix 16 is preferably made of a lower density open-cell polyurethane foam. Different materials can also be used for any of the components, but matrix 16 preferably has a lower compression modulus than inserts 18 and top layer 22, the purpose for which will be explained subsequently.
A section view representation of the present invention is shown in FIG. 2. The reader will observe that inserts 18 pass completely through matrix 16 so that the top of insert 18 is substantially flush with the top of bottom layer 14 and the bottom of insert 18 is substantially flush with the top of bottom layer 14. Inserts 18 are positioned substantially perpendicular to top layer 22, the purpose for which will be explained subsequently. Cover 20 encases cushion assembly 10 to protect the cushion and provide additional support.
The functionality of each of the layers will now be considered in greater detail. Cover 20 and top layer 22 transmit and distribute the compressive load across the top surface of cushion assembly 10. The load is transmitted through top layer 22 to middle layer 12, and bottom layer 14. Inserts 18 act as the principal support means for top layer 22. Inserts 18, based on their geometry, tend to both compress and buckle when subjected to compressive loading. Matrix 16 both provides additional support against compressive loading and provides resistance against inserts 18's tendency to buckle. Inserts 18 are preferably adhesively bonded within matrix 16. The adhesive integrates insert 18 and matrix 16 so that the components of bottom layer 14 act in unison. The adhesive further provides additional resistance to the buckling of inserts 18. Although matrix 16 and the adhesive provide resistance to buckling, the controlled buckling of inserts 18 is desirable as will be explained subsequently. Middle layer 12 functions to distribute the compressive load across the surface of bottom layer 14 and prevents bottom layer 14 from tearing.
Example geometries for insert 18 are shown in FIGS. 3A, 3B, and 3C. The preferred embodiment of insert 18, a rectangular prism, is shown in FIG. 3A. The reader will observe that insert 18 has a substantially square cross section. Narrowest effective width W denotes the narrowest side of the cross section. Since the cross section of insert 18 is preferably a square, narrowest effective width W describes all of the sides of the square cross section. If a rectangular cross section is used, narrowest effective width W would describe the shortest sides of the rectangular cross section. Height H describes the height of insert 18 when it is situated in its normal vertical orientation. In the preferred embodiment, height H is greater than narrowest effective width W to encourage insert 18 to buckle when subjected to a compressive load. Buckling occurs when insert 18 bends out-of-plane. Those that are skilled in the art know that this mode of failure is distinguishable from pure compression which involves longitudinal deflection with some degree of lateral bulging.
Other various angular or curvilinear cross-section geometries for insert 18 can be used, including but not limited to, triangular as shown in FIG. 3B and circular as shown in FIG. 3C. In FIG. 3B, narrowest effective width W describes the shortest side of the triangular cross section. In FIG. 3C, narrowest effective width W describes the diameter of the circle. While other geometries not shown or described herein can also be used, in each of these designs it is preferred that height H be greater than narrowest effective W to encourage buckling.
The relationship and integration between the various components of the present invention will be now considered together. As described previously (and as illustrated in FIG. 2), top layer 22 acts as a “loading plate” to distribute the compressive load across as much of the cushion as possible while still providing a responsive surface that is both supportive and comfortable. Although a more rigid top layer would distribute the compressive load across the top of cushion assembly 10 more evenly, it would not provide the desired responsive surface and could cause the user discomfort at various pressure points. Accordingly, a polyurethane foam having a high compression modulus is a good choice for top layer 22. Since matrix 16 generally has a lower compression modulus than inserts 18, inserts 18 act as principal support columns for the “loading plate.” Because inserts 18 are spread throughout matrix 16, cushion assembly 10 can be more responsive to uneven loading, thus eliminating discomfort caused by pressure points. For example, if cushion assembly 10 is used for a seat cushion, inserts 18 will compress and buckle to a greater degree under the points of higher loading such as the parts of the cushion supporting the user's legs and coccyx.
FIGS. 5-7 illustrate a “stratified” embodiment of the present invention. In this embodiment, alternating strata of foam material are arranged in a common horizontal plane and adhesively fixed together. In the preferred embodiment, each strata comprises a different material than its adjacent strata. FIG. 5 is an exploded view showing the various components of the stratified assembly. In the present example, the alternating strata of foam materials comprise visco-elastic strata 24 and open-cell strata 26. Visco-elastic strata 24 are strips of visco-elastic memory foam, and open-cell strata 26 are strips of open-cell polyurethane foam. Top layer 28 comprises a relatively soft material. It may be open-cell polyurethane foam, visco-elastic memory foam, or another type of foam.
It should be noted that visco-elastic memory foam materials possess physical characteristics that are different than most other foams. In particular, the “supportiveness” of a sample of visco-elastic memory foam is highly dependent on the temperature of the sample and the pressure exerted on the sample. As the sample is warmed, the foam provides less support.
As illustrated in FIG. 6, alternating strips of visco-elastic strata 24 and open-cell strata 26 are fixed together in a common horizontal plane with a foam adhesive. When arranged in this manner, each stratum has height H and narrowest effective width W. As with the previously described embodiments, it is preferred that height H be greater than narrowest effective width W to encourage buckling. As shown in FIG. 7, top layer 28 is then attached to the assembly with foam adhesive. Similar to top layer 22 in the previous embodiments, top layer 28 helps distribute load across multiple strata.
With the structure now described, the functionality of the embodiment of FIGS. 5-7 may be considered in greater detail. When the assembly is first loaded, visco-elastic strata 24 provides the majority of the support since the compression modulus is greater than that of open-cell strata 26. As pressure and temperature increase (as the user puts more weight on the cushion and the user's body transfers heat to the cushion), open-cell strata 26 begin to provide the majority of the support since its compression modulus is greater than that of the “pressed” and warmed visco-elastic strata 24. This transition of support between the strata enables the cushion to provide advantageous supportive properties that cannot be realized using exclusively visco-elastic memory foam or open-cell polyurethane foam. In particular, the cushion is more “responsive” when initially loaded that visco-elastic memory foam and more “supportive” than visco-elastic memory foam once compressed. That is, the stratified cushion feels “softer” than conventional visco-elastic foam cushions upon initial loading, but become slightly “firmer” than visco-elastic foam cushions as the load “indents” the cushion. These advantages are realized without causing pressure points or otherwise sacrificing comfort.
The stratified assembly offers further advantages over that afforded by cushions made exclusively of visco-elastic memory foam. For example, visco-elastic foam cushions tend to “trench” around the user's body making it difficult for the user to move around after sitting or lying in one place for an extended period of time. Open-cell strata 26 help transition the load around the user's body so that the user does not get the feeling that he or she is “trapped” in a crater. The use of open-cell strata 26 also allows cushions to be manufactured with a greater depth (corresponding to height H illustrated in FIG. 6) without having a corresponding increase in trenching effect.
In addition, the stratified assembly can be manufactured less expensively than current visco-elastic foam cushions since the stratified assembly uses approximately half the volume of visco-elastic memory foam as a conventional visco-elastic foam cushion. It has also been found that the proposed stratified assembly releases heat and moisture more quickly than cushions made entirely of visco-elastic foam. This is because open-cell strata 26 provide channels for air to migrate between visco-elastic strata 24. The movement of this transient air facilitates the flow of heat and moisture out of the cushion.
The preceding description contains significant detail regarding the novel aspects of the present invention. It should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As an example, inserts 18 can be spaced throughout matrix 16 in various configurations. Inserts 18 are presented in a simple grid format in FIG. 1, but alternating grid lines can also be used as shown in FIG. 4. Inserts 18 can also be placed in nonlinear format. Such a variation would not alter the function of the invention. Also, a single component may be used to perform the functions of the top and middle layer. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.